Actuator device for manipulating movable member

Abstract

In an actuator device which comprises a screw shaft, a nut member, and balls, the nut member moves relatively to the screw shaft in a first axial direction and a second axial direction opposite thereto in a manner such that it is continually subjected to a load in the first axial direction. A ball screw groove of the screw shaft is formed having a loaded surface which is pressed against the balls, on the side of a groove base in the first axial direction. A ball screw groove of the nut member is having a loaded surface which is pressed against the balls, on the side of its groove base in the second axial direction. These loaded surfaces are finished so that their surface roughness is lower than that of the unloaded surfaces.

1. An actuator device for manipulating a movable member, comprising:
 a screw shaft having a ball screw groove formed on an outer peripheral surface thereof;  
 a nut member located on the outer periphery of the screw shaft and having a ball screw groove formed on an inner peripheral surface thereof; and  
 a plurality of balls housed between the ball screw groove of the screw shaft and the ball screw groove of the nut member,  
 wherein the nut member moves relatively to the screw shaft in a first axial direction and a second axial direction opposite thereto in a manner such that the nut member is continually subjected to a load in the first axial direction; the ball screw groove of the screw shaft has a loaded surface, which is formed on a groove base thereof, which extends in the first axial direction and which is pressed against the balls by the load in the first axial direction, and an unloaded surface which is formed on the groove base and which extends in the second axial direction; the ball screw groove of the nut member has a loaded surface, which is formed on a groove base thereof, which extends in the second axial direction and which is pressed against the balls by the load in the first axial direction, and an unloaded surface which is formed on the groove base and which extends in the first axial direction,  
 the respective loaded surfaces and unloaded surfaces of the ball screw grooves, only the loaded surfaces are finished so that the surface roughness thereof is lower than that of the unloaded surfaces.  
 
   
   
     2. An actuator device for manipulating a movable member according to  claim 1 , wherein the surface roughness of the finished loaded surfaces is lower than the surface roughness of the machined unloaded surfaces. 
   
   
     3. An actuator device for manipulating a movable member according to  claim 2 , wherein the movable member is a movable pulley disk for a belt-type continuously variable transmission, and the belt-type continuously variable transmission has the cylindrical screw shaft fixed to a supporting member, the nut member provided on the outer periphery of the screw shaft, a rotating shaft inserted into the screw shaft, extending in the axial direction thereof and rotatable with respect to the screw shaft, a fixed pulley disk which rotates together with the rotating shaft, and the movable pulley disk provided on the rotating shaft to face the fixed pulley disk and to move together with the nut member in the axial direction of the rotating shaft. 
   
   
     4. An actuator device for manipulating a movable member according to  claim 1 , wherein the movable member is a movable pulley disk for a belt-type continuously variable transmission, and the belt-type continuously variable transmission has the cylindrical screw shaft fixed to a supporting member, the nut member provided on the outer periphery of the screw shaft, a rotating shaft inserted into the screw shaft, extending in the axial direction thereof and rotatable with respect to the screw shaft, a fixed pulley disk which rotates together with the rotating shaft, and the movable pulley disk provided on the rotating shaft to face the fixed pulley disk and to move together with the nut member in the axial direction of the rotating shaft.